Hi Henrik Rosén,
According to this problem, as per my knowledge, you may get rid of the prompt by two ways.
First, you ma rename your personal Microsoft account. You can rename your personal account, which means using a different email address to sign in to it. You can either create a new email address (alias) or set an existing email address to be your primary alias.
Your primary alias appears on devices, such as your Xbox, Surface, and Windows Phone, and is the email address that OneDrive sends from when you share things like photos or documents.
To rename your account, see Manage how you sign in to Microsoft.
Second, you may try to contact the organization. Where an organization's .com domain name matches that of your personal account, you can contact the other organization to ask them to remove your name from their email lists.
Your personal email address will not be in use or available to anyone in the other organization, but they simply need to "sync their users" to prevent this error from happening.
If you still need help, email the OneDrive support team. Or if you still have any problems about this issue, please come back and tell me, I'll help you at any time.
Have a nice day!
Regards,
Rebecca